Superfuzz Build - Poor Transistor Values

[killerkev]

Tried a Univox Superfuzz build and having some voltage issues. I followed the schematic listed here:



No substitutions were made with any component values, I used 2N222 transistors. Only additions were a 220 uf Electro Cap and diode for a power filter and a LED limiting resistor. Looks like I have a problem at both Q4 & Q5.Below are the measured voltages:

Battery – 9.35 V

Q1 C-5.10   Q2 C-9.28   Q3 C-5.87   
      B-0.70         B-5.10       B-3.91        
      E-0.14         E-4.51         E-3.34   

Q4 C-1.53   Q5 C-1.53   Q6 C-3.59
      B-2.00         B-2.03         B-1.16
      E-1.45         E-1.45         E-0.56

I touched both Q4 & Q5 transistor legs with the solder iron along with the 10 K & 1.8K resistor and the 10 uf electro cap that feed power and ground these transistors and no change. Any suggestions hopefully please?

[LucifersTrip]

I guess the first thing after checking voltages (which you did) would be to double check transistor orientation and surrounding resistor values. It's easy to mess up orientation since that's the back to back pair.  Btw, do you have all the 10uf's oriented correctly?

...and here're voltages from Solidhex's bandmate's original

C        B        E
Q1  6.01    .66      .117
Q2  8.88   6.01     5.41
Q3  6.23   3.27     2.72
Q4  3.1     1.7      1.11
Q5  3.1     1.67     1.11
Q6  5.75   .98       .361

[killerkev]

I made sure when I put each tranny in that the orientation was correct but will look at these two transistors again to make sure. I also made sure that each one of the electros were put in correctly, double checked it again an it is. The 10K resistor that feeds these two trannies was measure before putting it in the PCB and checked once again. Could it be a grounding issue? I did re-hit all of these components with flux and iron

[Keppy]

Don't forget to check the 1.8k emitter resistor, and make sure the 10uF isn't leaky.

On Q4 & Q5 your bases and emitters are high, but only a little. The collectors are way too low (lower than the bases), meaning the transistors are too "on," meaning they're sucking in too much current. Such a thing could happen if the 1.8k resistor is too low, or the cap is very leaky. If you suspect the cap, you can remove it. The DC voltages should remain the same if the cap is good.

[killerkev]

Don't forget to check the 1.8k emitter resistor, and make sure the 10uF isn't leaky.

On Q4 & Q5 your bases and emitters are high, but only a little. The collectors are way too low (lower than the bases), meaning the transistors are too "on," meaning they're sucking in too much current. Such a thing could happen if the 1.8k resistor is too low, or the cap is very leaky. If you suspect the cap, you can remove it. The DC voltages should remain the same if the cap is good.

Thanks! That's some of the details and explanation I was hoping for. Will check all of the above and report back hopefully tonight. Dying to get this thing working. Pete Townsend...Live at Leeds! Yea baby!

[killerkev]

Boo Hoo. Still no change. Checked the orientation of Q4 & Q5 and they are correct. Changed out the 10K resistor that feeds these two trannies with anothe rbrand new one. No change. Changed the emittor 1.8K resistor to a 2.2K an had these changes:
Q4 C-1.77

[killerkev]

Ops, something happened and my reply posted before intended. Anyway after changing the emitter resistor to 2.2K from 1.8 K I have these voltages:

Q4 C-1.77     Q5 C -Same
     B-2.14          B- Same
     E-1.66          E-Same

Still no good. I took the adjustable 10K resistor out of the loop and put a 5K resistor in and got these votages:

Q4 C-1.9     Q5 C -1.9
     B-2.45          B- 1.93
     E-1.86          E-1.85

No Live at Leeds for me tonight.

So any increase in collector voltage resulted in an increase in both Base and emitter voltage.

[killerkev]

And also changed the 10uf electro cap (oriented correctly) with another brand new one and still no change

[Keppy]

after changing the emitter resistor to 2.2K from 1.8 K I have these voltages:

Q4 C-1.77     Q5 C -Same
     B-2.14          B- Same
     E-1.66          E-Same

Well, your collector voltage rose a little. That's something.

I took the adjustable 10K resistor out of the loop and put a 5K resistor in

What? I don't see an adjustable resistor. What do you mean? Are you talking about the Q4/Q5 collector resistor?

So any increase in collector voltage resulted in an increase in both Base and emitter voltage.

That should not happen, because your base and emitter voltages are determined independently by the bias network (100k & 22k on each base). This implies:

1) A mistake in your build involving those resistors (unlikely unless you made the same mistake twice)

2) A problem with the coupling caps that messes up your DC conditions (though I can't think what problem would cause those particular voltages)

3) Faulty or misused transistors. I think you're at the point of subbing these out, right after you

4) Check the OTHER end of the collector resistor to make sure there's really 9v on it. There is, right?

[killerkev]

Yes, there is a added adjustable resistor (10K) between the 470 ohm and 22K resistor which is not on this schematic which controls the octave effect. Some superfuzzes had these adjustable resistors. Yes, the 10K resistor feeding volage to these two Q's does show the battery value but drops once measured on the other side.

[DiscoVlad]

Here's an excerpt from the factory schematic (which I'm assuming you worked from) showing Q4 and Q5 with some ballpark voltages for both.



Things to note:
The wiper of the trimpot IS NOT is connected to the base of either Q4 or Q5.
Your collector voltage is still lower than the base -> The transistor won't conduct. Look for solder bridges (clean the flux off too as this can hide short circuits).
Check the pinout (diode check/HFE function on multimeter) - I've had 2n2222 (TO-92 version) transistors from one supplier which were mixed ECB and EBC pinout from two manufacturers. If you're using the metal can (TO-18) type the emitter is next to the tab, and the base is in the centre of the three leads.

Remove the transistors and check voltages:
The voltages at the Base - the junction of the 470, 22k and 100k resistors shouldn't change.
The Collector voltage (10k resistor) should read 9V on both sides as it's pulled up to the 9v rail.
The Emitter (1.8k resistor) should read 0V on both sides as it's pulled down to ground.

[killerkev]

Here's an excerpt from the factory schematic (which I'm assuming you worked from) showing Q4 and Q5 with some ballpark voltages for both.



Things to note:
The wiper of the trimpot IS NOT is connected to the base of either Q4 or Q5.
Your collector voltage is still lower than the base -> The transistor won't conduct. Look for solder bridges (clean the flux off too as this can hide short circuits).
Check the pinout (diode check/HFE function on multimeter) - I've had 2n2222 (TO-92 version) transistors from one supplier which were mixed ECB and EBC pinout from two manufacturers. If you're using the metal can (TO-18) type the emitter is next to the tab, and the base is in the centre of the three leads.

Remove the transistors and check voltages:
The voltages at the Base - the junction of the 470, 22k and 100k resistors shouldn't change.
The Collector voltage (10k resistor) should read 9V on both sides as it's pulled up to the 9v rail.
The Emitter (1.8k resistor) should read 0V on both sides as it's pulled down to ground.

Yes, I just downloaded that schematic to post to show the trim pot but you bet me to it! Yes, I had checked the transistor before I had put them in. They are from the same manufacturer and are TO-18 style with the emitter tab. I do have some new untouched extras that I will put in after performing the other tests you described. be back in 30 minutes with results

[PRR]

Does it play??

2V on the pair's bases is wrong. With transistors out, batt at 9.35V, these points should be 1.686V. Lower with transistors in. Suspect leaking (backward) caps or mis-read resistor values.

The trim-pot is a frill. Don't do it; or short all three pot-pins together until it plays pretty-good and you need that last bit of tweak.

[pedal parts]

i've just check the V on my build - with the trim pins shorted, supply at exactly 9V:

Q4 + 5

C 3.6
B 1.6
E .9

with trim pot in centre position and not shorted out

C 2.2
B 1.9
E 1.2

[killerkev]

In response to DiscoVlad suggested troubleshooting:•   Yes, the trimpot is not connected to the base of either Q4 & Q5
•   I removed Q4 & Q5 and cleaned thoroughly to remove all flux.
Remove the transistors and check voltages:
The voltages at the Base - the junction of the 470, 22k and 100k resistors shouldn't change. The voltages stayed the same – 2.17 v
The Collector voltage (10k resistor) should read 9V on both sides as it's pulled up to the 9v rail. It did – 8.84VThe Emitter (1.8k resistor) should read 0V on both sides as it's pulled down to ground. It did – 0V

In response to PRR suggested troubleshooting:

Does it play?? I actually have not plugged it in. After finishing the build I tested the trannies and knew I had a problem with Q4 & Q5.
2V on the pair's bases is wrong. With transistors out, batt at 9.35V, these points should be 1.686V. Lower with transistors in. Suspect leaking (backward) caps or mis-read resistor values.  Yes, the voltages are wrong! Your suggestion goes against what DiscoVlad suggested with the transistors out of the loop. I had inspected each orientation of all brand new electro caps and brand new resistor and even tested their resistance before placing them in the PCB, I took my time populating this board!
The trim-pot is a frill. Don't do it; or short all three pot-pins together until it plays pretty-good and you need that last bit of tweak. I tested with the trimpot and without (jumper) with no change in voltages

In response to Pedal Parts comment:


i've just check the V on my build - with the trim pins shorted, supply at exactly 9V:

Q4 + 5

C 3.6
B 1.6
E .9

So what do you think is my problem? I wish I had those readings!

with trim pot in centre position and not shorted out

C 2.2
B 1.9
E 1.2
I've removed the trimpot with a jumper but have had no improvement.

[DiscoVlad]

In response to DiscoVlad suggested troubleshooting:•   Yes, the trimpot is not connected to the base of either Q4 & Q5
•   I removed Q4 & Q5 and cleaned thoroughly to remove all flux.
Remove the transistors and check voltages:
The voltages at the Base - the junction of the 470, 22k and 100k resistors shouldn't change. The voltages stayed the same – 2.17 v
The Collector voltage (10k resistor) should read 9V on both sides as it's pulled up to the 9v rail. It did – 8.84VThe Emitter (1.8k resistor) should read 0V on both sides as it's pulled down to ground. It did – 0V

This suggests to me that there's a problem with the transistors (backwards, wrong pinout, damaged, etc). I'd check the pinout with the diode/hfe check on a multimeter (just in case the datasheet is leading you astray).

Have you tried to breadboard up the biasing for Q4 (100k + 22k on base, 10k on collector, and 1.8k on the emitter) and measured/compared from that?
Also check with different transistors of which you are 100% certain of the pinout, and which you know work.

[pedal parts]

can i just check what's going on with your trimpot / lack of trimpot? do you have the two outer pads connected to the centre pad with jumpers? if you're removed the trimpot you need to do this to ground the 22k resistors from bases of Q4 & 5.
sorry if that sounds obvious, but it isn't clear what you have jumpered.

i don't think i've ever measured voltages on something before plugging it in and trying it. i trust my ears over numbers any day of the week.

[killerkev]

This suggests to me that there's a problem with the transistors (backwards, wrong pinout, damaged, etc). I'd check the pinout with the diode/hfe check on a multimeter (just in case the datasheet is leading you astray).

Have you tried to breadboard up the biasing for Q4 (100k + 22k on base, 10k on collector, and 1.8k on the emitter) and measured/compared from that?
Also check with different transistors of which you are 100% certain of the pinout, and which you know work.

I placed brand new 2N222 transistors back in for Q4 & Q5 after performing the test you suggested with the trannies out. I checked the pinout of each with my DMM, they have steady hfe readings of about 250. Plus, all of the other trannies are the same type and there does not seem to be a problem with the other voltages.

No, I haven't thought of breadboarding this portion of the circuit. I guess it's something to try to see what values come up. I could play with other transistors like a 2N5088 just to see what happens.

[killerkev]

can i just check what's going on with your trimpot / lack of trimpot? do you have the two outer pads connected to the centre pad with jumpers? if you're removed the trimpot you need to do this to ground the 22k resistors from bases of Q4 & 5.
sorry if that sounds obvious, but it isn't clear what you have jumpered.

i don't think i've ever measured voltages on something before plugging it in and trying it. i trust my ears over numbers any day of the week.

No, I had use a piece of wire to connect the two outer pads only and left the center alone, I wil change that tonight. Normally I check tranny voltages after a build since it's quick to see iff they are behaving properly. Gonna plug it in some time today before the kids go to bed!

[killerkev]

I plugged it into an amp and played throught it. There is a huge volume drop when engaged and I can hear the effect but it is seriously gated. Sounds like it could be awesome if I can get rid of the gating and volume drop!